Briefly stated, the present invention relates to seat belt webbing, and more particularly to an improved method for manufacturing seat belt webbing having both high lateral stiffness and specialty edging. Seat belt (also called safety belt) systems have evolved significantly as these systems have become standard equipment in all types of automotive vehicles. Different designs of seat belts have been provided for various types of systems, depending upon the properties desired. Automobile manufacturers may specify a preference for one desirable property over another, and certain automobile designs suggest that a desirable webbing would have a round or other specialty edge to provide added passenger comfort. Sometimes, automobile manufacturers may specify a round or other specialty edge in conjunction with webbing having a high lateral stiffness. The lateral stiffness is desirable because it can help prevent roping or twisting of the seat belt, such as within the "D" ring upon extraction or retraction which could lead to a malfunction of the seat belt system.
One means to provide high lateral stiffness is to manufacture a seat belt webbing using two different types of weft yarns, such as multifilament and monofilament yarns. Several designs and processes presently exist for the manufacture of this type of product; however, these designs and processes insert both types of weft yarns simultaneously through the shed. These designs and processes can be difficult to manufacture and to maintain good quality control because the tension relationship between two weft yarns, the catch cord yarn, and the lock stitch yarn is critical to the proper formation of the webbing's edges. This is especially true at high manufacturing speeds and thus has an impact on the performance of the manufacturing equipment. The present invention, whereby two groups of weft yams are inserted on alternate passes or picks rather than inserted in the same pick, yields a webbing that is easier to manufacture because the resultant weft and warp tensions are not as critical to the formation of a round or other specialty edge as compared to existing methods, especially when used with larger denier weft yarns which are more difficult to fold into a round edge at high manufacturing speeds. This results in fewer manufacturing defects.